1. Field of the Invention
The present invention relates to a fault localization apparatus based on an optical communication network and a method thereof, and more particularly, to a fault localization apparatus for an optical line using a downstream light source as a monitoring light source instead of using an additional monitoring light source, and a method thereof.
The present invention was supported by the Information Technology (IT) Research & Development (R&D) program of the Ministry of Information and Communication (MIC) [Project management number: 2005-S-401-02, Project title: Optical Subscriber and Access Network Technology].
2. Description of the Related Art
An x digital subscriber line (xDSL) technology has been developed and is being currently used to provide data services to a subscriber by using a conventional telephone line. As well as this, a technology for data services by a cable network using a coaxial cable has been suggested and is currently being developed.
The above conventional technologies for data services do not seem to have any major problems in consideration of the amount of Internet traffic currently used by a subscriber. However, assuming that super-high-speed data services such as telecommuting, teleconferencing, services of moving pictures having as high quality as high-definition televisions (HDTVs), tele-education, and telemedicine services are generalized to common subscribers, the conventional technologies may not provide sufficiently high quality services for a broadband due to their restrictions in terms of bandwidths and distances.
An optical communication network technology is regarded as a conspicuous access method of providing sufficient broadband services to subscribers.
Optical fibers which are transmission media of optical signals used for the optical communication network, are buried under the ground and thus may be relatively easily cut or damaged by an external impact such as a natural calamity or construction which may impact the ground, compared to copper cables which are transmission media of electrical signals. If communication services to subscribers are discontinued due to one of the above reasons, this may reduce reliability of the communication network and may also reduces customer satisfaction. Therefore, when a fault occurs in the optical fibers, it is vital to find the position of the fault promptly and accurately so as to repair the fault.
A convention thesis entitled ‘Optical Maintenance in passive optical networks (PONs)’ (European Conference on Optical Communication, Vol 1, pp. 621-625, 20-24 Sep. 1998) discloses a technology that an optical time domain reflectometer (OTDR) having a light source for generating a monitoring wavelength different from a communication wavelength is included in a central base station and an optical band pass filter (BPF) for attenuation of the monitoring wavelength is disposed in front of an optical line terminal (OLT) so that a reflected light signal of the monitoring wavelength does not reach the OLT of the central base station.
According to the above technology, when a fault occurs in an optical line, an OTDR optical pulse signal transmitted as the monitoring wavelength is almost completely reflected from the position of the fault so that fault localization may be performed on the optical line. However, the above technology requires an additional monitoring light source and an additional optical BPF for attenuation of the monitoring light source and thus has a problem from an economical aspect.
Also, recently, research on fault localization apparatuses for an optical line in a wavelength division multiplexed-passive optical network (WDM-PON) which is regarded as a next generation optical communication network has been actively conducted. US Patent Publication No. 20060222364 entitled ‘Fault localization apparatus for optical line in wavelength division multiplexed passive optical network’ discloses a method of receiving upstream signals, checking a channel having a fault by whether a signal is input to a receiving terminal, operating a controller, and using a downstream light source which is normally used for data transmission as a monitoring light source by a switch.
A monitoring optical pulse signal generated by using the above method is inserted in the optical line and backward-scattered light is received by an OTDR receiver through an optical circulator and a tunable BPF. However, although the above method does not use an additional monitoring light source, the expensive tunable BPF is necessary to receive monitoring optical pulse signals.